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      Green Pesticides: Essential Oils as Biopesticides in Insect-pest Management

      Journal of Environmental Science and Technology
      Science Alert

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          Pesticide Exposure, Safety Issues, and Risk Assessment Indicators

          Pesticides are widely used in agricultural production to prevent or control pests, diseases, weeds, and other plant pathogens in an effort to reduce or eliminate yield losses and maintain high product quality. Although pesticides are developed through very strict regulation processes to function with reasonable certainty and minimal impact on human health and the environment, serious concerns have been raised about health risks resulting from occupational exposure and from residues in food and drinking water. Occupational exposure to pesticides often occurs in the case of agricultural workers in open fields and greenhouses, workers in the pesticide industry, and exterminators of house pests. Exposure of the general population to pesticides occurs primarily through eating food and drinking water contaminated with pesticide residues, whereas substantial exposure can also occur in or around the home. Regarding the adverse effects on the environment (water, soil and air contamination from leaching, runoff, and spray drift, as well as the detrimental effects on wildlife, fish, plants, and other non-target organisms), many of these effects depend on the toxicity of the pesticide, the measures taken during its application, the dosage applied, the adsorption on soil colloids, the weather conditions prevailing after application, and how long the pesticide persists in the environment. Therefore, the risk assessment of the impact of pesticides either on human health or on the environment is not an easy and particularly accurate process because of differences in the periods and levels of exposure, the types of pesticides used (regarding toxicity and persistence), and the environmental characteristics of the areas where pesticides are usually applied. Also, the number of the criteria used and the method of their implementation to assess the adverse effects of pesticides on human health could affect risk assessment and would possibly affect the characterization of the already approved pesticides and the approval of the new compounds in the near future. Thus, new tools or techniques with greater reliability than those already existing are needed to predict the potential hazards of pesticides and thus contribute to reduction of the adverse effects on human health and the environment. On the other hand, the implementation of alternative cropping systems that are less dependent on pesticides, the development of new pesticides with novel modes of action and improved safety profiles, and the improvement of the already used pesticide formulations towards safer formulations (e.g., microcapsule suspensions) could reduce the adverse effects of farming and particularly the toxic effects of pesticides. In addition, the use of appropriate and well-maintained spraying equipment along with taking all precautions that are required in all stages of pesticide handling could minimize human exposure to pesticides and their potential adverse effects on the environment.
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            Mechanism of action of insecticidal secondary metabolites of plant origin

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              Thymol, a constituent of thyme essential oil, is a positive allosteric modulator of human GABA(A) receptors and a homo-oligomeric GABA receptor from Drosophila melanogaster.

              The GABA-modulating and GABA-mimetic activities of the monoterpenoid thymol were explored on human GABAA and Drosophila melanogaster homomeric RDLac GABA receptors expressed in Xenopus laevis oocytes, voltage-clamped at -60 mV. The site of action of thymol was also investigated. Thymol, 1-100 microm, resulted in a dose-dependent potentiation of the EC20 GABA response in oocytes injected with either alpha1beta3gamma2s GABAA subunit cDNAs or the RDLac subunit RNA. At 100 microm thymol, current amplitudes in response to GABA were 416+/-72 and 715+/-85% of controls, respectively. On both receptors, thymol, 100 microm, elicited small currents in the absence of GABA. The EC50 for GABA at alpha1beta3gamma2s GABAA receptors was reduced by 50 microm thymol from 15+/-3 to 4+/-1 microm, and the Hill slope changed from 1.35+/-0.14 to 1.04+/-0.16; there was little effect on the maximum GABA response. Thymol (1-100 microm) potentiation of responses to EC20 GABA for alpha1beta1gamma2s, alpha6beta3gamma2s and alpha1beta3gamma2s human GABAA receptors was almost identical, arguing against actions at benzodiazepine or loreclezole sites. Neither flumazenil, 3-hydroxymethyl-beta-carboline (3-HMC), nor 5alpha-pregnane-3alpha, 20alpha-diol (5alpha-pregnanediol) affected thymol potentiation of the GABA response at alpha1beta3gamma2s receptors, providing evidence against actions at the benzodiazepine/beta-carboline or steroid sites. Thymol stimulated the agonist actions of pentobarbital and propofol on alpha1beta3gamma2s receptors, consistent with a mode of action distinct from that of either compound. These data suggest that thymol potentiates GABAA receptors through a previously unidentified binding site.
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                Author and article information

                Journal
                Journal of Environmental Science and Technology
                J. of Environmental Science and Technology
                Science Alert
                19947887
                May 1 2016
                May 1 2016
                : 9
                : 5
                : 354-378
                Article
                10.3923/jest.2016.354.378
                14a30acc-4c48-48cf-96ff-b76f7d4a6b1b
                © 2016
                History

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